Fluorescence correlation spectroscopy for the characterisation of drug delivery systems

Shining Light on Polymeric Drug Nanocarriers with Fluorescence Correlation Spectroscopy

The use of nanoparticles as carriers is an extremely promising way for administration of therapeutic agents, such as drug molecules, proteins and nucleic acids. Such nanocarriers (NCs) can increase the solubility of hydrophobic compounds, protect their cargo from the environment, and if properly functionalized, deliver it to specific target cells and tissues. Polymer-based NCs are especially promising, because they offer high degree of versatility and tunability. However, in order to get a full advantage of this therapeutic approach and develop efficient delivery systems, a careful characterization of the NCs is needed. This Feature Article highlights the fluorescence correlation spectroscopy (FCS) technique as a powerful and versatile tool for NCs characterization at all stages of the drug delivery process. In particular, FCS can monitor and quantify the size of the NCs and the drug loading efficiency after preparation, the NCs stability and possible interactions with, e.g., plasma proteins in the blood stream and the kinetic of drug release in the cytoplasm of the target cells. This article is protected by copyright. All rights reserved.

Molecular design of a high-performance polymeric carrier for delivery of a variety of boronic acid-containing drugs

Because of their many useful and unique properties, boronic acids are well suited for biomedical applications such as antitumor chemotherapy and boron neutron capture therapy (BNCT). Bortezomib, a boronic acid derivative, has drawn a lot of attention as a potent proteasome inhibitor. Nevertheless, because of rapid excretion and off-target effects, the clinical translation of boronic acid-containing drugs is limited. To this end, we employed a polymeric carrier to stably encapsulate boronic acid-containing drugs and achieve superior pharmacokinetics with an on-target drug release capability. Accordingly, to construct a supramolecular polymeric nanoparticle, we took advantage of the facile, stable, and pH-sensitive conjugation between boronic acids and diethanolamine-installed polymeric carriers. We demonstrated the feasibility of our molecular design by generating and applying bortezomib-loaded nanoparticles to a subcutaneous tumor-bearing mouse model. Stable encapsulation and pH-sensitive release of bortezomib facilitated antitumor efficacy and alleviated hepatotoxicity. We also verified the versatility of our approach through biological evaluations of the nanoparticles encapsulating benzo(b)thiophene-2-boronic acid, phenylboronic acid, and p-phenylene-diboronic acid.

Study of interaction of hypericin and its pharmaceutical preparation by fluorescence techniques

We report the detection of interactions between a photosensitizer, hypericin (HY), and its solvent system prepared with a formulation additive, polyvinylpyrrolidone (PVP), a commonly used pharmaceutical excipient. Fluorescence correlation spectroscopy (FCS) and fluorescence lifetime imaging microscopy (FLIM) were used to study aggregation and binding of HY in the presence of PVP. Digitized fluorescence endoscopic imaging (DFEI) was used to study the effect of the pharmaceutical formulation in the in vivo tumor implanted chick chorioallantoic membrane (CAM) model. The results presented reveal the coordination of HY-PVP binding, HY disaggregation in the presence of PVP, and strengthened HY tumor uptake selectivity. PVP is thus suggested as a potential adjuvant to previously investigated N-methyl pyrrolidone (NMP) in the HY delivery system as well as a replacement for the conventionally used albumin in the HY bladder instillation fluids preparation for clinical use.

Drug delivery of oligonucleotides by peptides

Oligonucleotides are promising tools for in vitro studies where specific downregulation of proteins is required. In addition, antisense oligonucleotides have been studied in vivo and have entered clinical trials as new chemical entities with various therapeutic targets such as antiviral drugs or for tumour treatments. The formulation of these substances were widely studied in the past. With this review we will focus on peptides used as drug delivery vehicles for oligonucleotides. Different strategies are summarised. Cationically charged peptides from different origins were used e.g. as cellular penetration enhancers or nuclear localisation tool. Examples are given for Poly-L-lysine alone or in combination with receptor specific targeting ligands such as asialoglycoprotein, galactose, growth factors or transferrin. Another large group of peptides are those with membrane translocating properties. Fusogenic peptides rich in lysine or arginine are reviewed. They have been used for DNA complexation and condensation to form transport vehicles. Some of them, additionally, have so called nuclear localisation properties. Here, DNA sequences, which facilitate intracellular trafficking of macromolecules to the nucleus were explored. Summarizing the present literature, peptides are interesting pharmaceutical excipients and it seems to be feasible to combine the specific properties of peptides to improve drug delivery devices for oligonucleotides in the future.

Physicochemical characterisation of cationic polybutylcyanoacrylat-nanoparticles by fluorescence correlation spectroscopy

The aim of this study was to compare different physical and chemical methods with fluorescence correlation spectroscopy (FCS) in order to characterise cationic acrylate nanoparticles (NP), which can deliver oligonucleotides (ON) into mammalian cells. These positively charged nanoparticles were prepared from diethylaminoethyl dextran (DEAE-dextran) and poly(n-butyl-2-cyanoacrylate) (PBCA). NP consists of PBCA oligochains with an average size of PBCA 9 mer and were formed by entrapping DEAE-dextran and dextran 70,000 in high amounts into the particle matrix. The oligochain length of PBCA was investigated by mass-spectroscopy (MALDI TOF). The molecular weight of a particle with d = 108 nm was estimated to be approximately 3.6 x 10(8) Da. The mean size of the nanoparticles were in a range of dh = 130-140 nm, as determined independently by FCS and dynamic light scattering. Atomic force microscopy and scanning electron microscopy images confirm this size range. Furthermore, the particle mass of the PBCA-NP was estimated by FCS measurements. For this approach two new methods for fluorescence labelling of cationic particles were developed. Fluorescent labelled dextran 70,000 was entrapped into the particle matrix; in addition, the derivatisation of hydroxyl groups of the NP was achieved with 5-([4,6-dichlorotriazin-2-yl]amino) fluorescein (DTAF). ON can be localised in a complex with the NP by dual-colour fluorescence cross correlation spectroscopy measurements. The zetapotential of the unloaded NP was positively charged with about +39 mV and decreased down to -40 mV on addition of excess ON. After centrifugation quantification of the ON loading onto the particles by strong anion exchange high performance liquid chromatography (SAX HPLC) and FCS showed that approximately 20 microg ON per 100 g NP was adsorbed. The FCS measurements of the ON adsorption in situ was found to be much higher with approximately 95 microg ON per 100 g NP.